Papers

Researchers at Stanford University have successfully developed a brand new concept of organic lighting-emitting diodes (OLEDs) with a few nanometers of graphene as transparent conductor. This paves the way for inexpensive mass production of OLEDs on large-area low-cost flexible plastic substrates, which could be rolled up like wallpaper and virtually applied anywhere you want.

Due to its superb image quality, low power consumption and ultra-thin device structure, OLEDs have been developed for more than 20 years, and is recently applied in ultra-thin televisions and other display screens such as those on digital cameras and mobile phones. OLEDs consist of active organic luminescent structure sandwiched between two electrodes, one of which must be transparent. Traditionally, indium tin oxide (ITO) is used in this type of devices. However, indium is rare, expensive and difficult to recycle. Scientists have been actively searching for an alternative candidate.

The next generation of optoelectronic devices requires transparent conductive electrodes to be lightweight, flexible, cheap, environmentally attractive, and compatible with large-scale manufacturing methods. Graphene, a single layer of graphite, is becoming a very promising candidate due to its unique electrical and optical properties. Very recently, Junbo Wu et al., researchers at Stanford University, successfully demonstrated the application of graphene in OLEDs for the first time.

Junbo Wu, the leading researcher of the development, said that they achieved OLEDs on graphene with performance similar to a control device on conventional ITO transparent anodes, which is very exciting and promising for real-world applications. ‘The current report by Wu et al. puts forward a strong case for graphene as a transparent conductor given its competitive performance, even with significantly high sheet resistance.’ said Chongwu Zhou, professor at University of Southern California in the Perspective of ACS Nano, 4(1), 2010.

‘Graphene has the potential to be a transparent electrode with higher performance, which means it is more transparent and more conductive. It could also be orders of magnitude cheaper than conventional transparent conductors, like ITO. It really has the potential to be both better and cheaper.’ said Prof. Peter Peumans in Podcast Episode 30, ACS Nano January 2010. ‘It (graphene) does have an additional advantage that the electrode is very thin, only a couple of nanometers thick, which potentially gives you much more freedom to design your devices.’ Peter also added.

This research sheds light on the enormous potential of graphene, and opens up an entirely new avenue towards the development of efficient and economical transparent conductors for flexible optoelectronic devices, such as OLEDs and organic photovoltaic cells. Transferring of large-area graphene thin film to a foreign flexible substrate has been previously demonstrated. Combining these technologies together, we have good reasons to expect graphene OLED products on flexible plastic in the near future.

Nice work by the Fuhrer group on ArXiv. Transfer printing has been used to transfer graphene from the Standard Si/SiO2 substrate to a plastic substrate. In following steps a complete top-gated transistor has been assembled. Link

Emtsev et. al. present an approach to wafer-scale graphene on SiC in their new manuscript. Mobilities are in the range of ~ 1000 cm2/Vs at room temperature so one will need wait for further results (compare strained Si, etc. …). Yet, a big step towards the industrial use of graphene.

Echtermeyer et. al. report about the surface functionalization of graphene - which allows them to switch between a metallic and an insulating state. A method to engineer a band-gap in graphene without structuring it into sub-10 nm ribbons? Possible application might be nonvolatile memories.

Yu et. al. deposited graphene on a flexible substrate and introduced strain in graphene by simply bending the substrate. Raman spectroscopy was carried out to investigate the effect of strain. Possible applications might be strain sensors and band-gap engineering in graphene.